Molded plastic parts are used extensively in many products and assemblies. As known to those skilled in the art, maintaining relative consistency in thickness can improve surface finish. So called “divots” or “sinks” can be formed in a surface opposite to an extension or projection. In some situations the presence of a surface divot or sink is of no consequence. However, when surface finish is important, a sink or divot may be unacceptable. Hollowing the interior of a large or thick part can avoid the formation of a sink or divot by establishing greater consistency in thickness of the part along the visible surface for which surface finish is important.
Hollowing a part also reduces the weight of the part, which can be important and advantageous for a part that is lifted, moved or otherwise manipulated during use. Hollowing a part can also improve strength by establishing an interior surface for the molded part, which improves overall strength of the part.
Automobile door handle assemblies can take advantage of the aforementioned qualities, including improved surface finish, reduced weight and improved strength achieved by hollowing thicker portions of the handle components. Processes to hollow some types of parts, including vehicle door handle components, have met with some success; however the processes have not always been efficient or consistent. In some processes, hollowing is achieved by injecting an inert gas, such as nitrogen, into the still molten material through a gas inlet and forcing or displacing an interior volume of the still-molten material through an evacuation site. Locating the gas injection site and the molten material evacuation site can be difficult. Localized curing or hardening can block the injection and evacuation sites. In some processes, multiple gas injection sites or material evacuation sites have been needed. As a result, hollowing can be inconsistent, leading to finished surface irregularities, parts with localized weaknesses or parts with uneven weight distributions.
In a variation of the aforedescribed gas injection evacuation process, sometimes referred to as a “short shot” process, molten material is injected to partially fill the mold, followed by a shot of injected inert gas to create a hollow in the material of the first shot. This is then followed by another shot of molten material to further fill the mold, with an additional shot of the inert gas to hollow the second portion of filled material. This variation can lead to further irregularities as cooling occurs along the interface between shots of molten material, and cooling also can cause the material to pull away from the tool surface, thereby creating other types of surface irregularities.
Accordingly, a process to produce hollowed parts of injection molded plastic that provides design flexibility, consistency and improved surface finish will provide advantages.